Iridium Oxide Inverse Opal Anodes with Tailored Porosity for Efficient PEM Electrolysis

Abstract Proton exchange membrane water electrolysis (PEM‐WE) is one of the most promising industrial processes for the generation of green hydrogen. The harsh operating conditions demand highly corrosion‐resistant materials. For the anodic oxygen evolution reaction (OER), typically, the rare metal iridium is employed. In order to increase the economic viability of PEM‐WE, the reduction in the use of iridium is necessary. According to the recent literature, hard‐templated materials based on iridium offer a promising path to accomplish that. Here the development of a synthetic protocol toward porous Ir inverse opal (Ir‐IO) bulk catalyst materials, which allow control of the resulting chemical Ir state of the Ir‐IO, is reported. Two general modes of the same synthetic approach are compared and it is combined with a variety of heating procedures. This enables not only to achieve the targeted synthesis of each material, but also derive a molecular mechanistic hypothesis accounting for the chemical characteristics of the Ir‐IO materials. Furthermore, electrochemical characterization is performed, both on RDE as well as at the single‐cell level showing a reduction of the overall cell voltage of 80 mV @ 2 A cm⁻ 2 compared to a commercial reference material while using only a quarter of the iridium loading.